Drosophila Melanogaster, incomplete gene
Gene mapping is the process of assigning gene to specific chromosomes or specific loci on that chromosome. It also determines the relative distance between genes linked on the same chromosome (Strachan & Read 2004). Gene mapping is used to construct linkage map that shows the relative locus of all genes on each chromosome. This allows discovery of genetic markers or DNA sequences that are readily identifiable under microscope observation. By doing so, locations of critical genetic elements that are responsible for a disease could be identified. In humans, information of inheritance pattern and disease system obtained solely from pedigree analysis are limited, as sufficient progeny are not available to give reliable confirmation on characteristics and inheritance mode of disease-causing genes. Missing individuals or erroneous information in the pedigree further hinders analysis. Modern genetic linkage are particularly useful, as it can be examined in collaboration with pedigree to maximize information that can be collected to infer likely genotypes of any missing individuals.
According to Mendel's principle of independent assortment, pairs of alleles for a gene are assorted independently into gametes during meiosis, independent of other genes. This means that the behavior of one allele on one chromosome is unaffected by that of another allele on different chromosomes, giving a typical 9:3:3:1 phenotypic ratio for dihybrid crosses. However, it only considers segregation of genes located on different chromosomes.
[...] Lastly, genetic mapping technique dictated the success of Human Genome Project which was completed in year 2004. A collaborated effort by international scientists, base sequence and all genes of human DNA were mapped completely and information are beneficial to many fields such as medicine and evolutionary studies. As aforementioned, this genome project allows us to better understand the cause of diseases and from there we can device effective treatments. Medications can be designed and their effects can be accurately predicted by looking at the molecular pathway associated with particular genes. [...]
[...] Full dihybrid cross date for Chromosome X linkage: Table 30: Number of F1 progeny resulting from cross between P11 (wild type female) and P12 (forked bristle, incomplete wing vein male) with respect to their phenotypes and sex. All F1 progeny had wild type eye and wing vein. No forked bristle, incomplete wing vein flies were observed. Table 31: Number of F2 progeny resulting from test cross between F1 wild type female and P12 (forked bristle, incomplete wing vein male) with respect to their phenotypes and sex. The ratio of dihybrid testcross for the forked bristle gene and incomplete wing vein gene follows the expected Mendelian's inheritance ratio of 1:1:1:1. [...]
[...] Table 22: Chi-square test of F2 progeny resulted from cross between F1 wild type female and P4 (black body, incomplete wing vein male). The null hypothesis was that the incomplete wing vein gene and black body gene were unlinked, and independently assorted. Degree of freedom = 4-1 = 3 Level of significance = 0.8334 Since the level of significance ( 0.8334 ) was greater than the threshold the null hypothesis was not rejected. The ratio of dihybrid testcross for the black body gene and incomplete wing vein gene followed the expected Mendelian's inheritance ratio of 1:1:1:1. [...]
[...] As such, the incomplete wing vein gene was also not linked to dumpy wing gene and brown eye gene. It was not located on chromosome 2. Refer to appendix for full test. Dihybrid cross to determine linkage on chromosome 3. For chromosome selected marker was ebony body gene. Dihybrid cross between flies with wild type body, wing vein and flies with black color body, incomplete wing vein was conducted. P5: Pure breeding parent strain with wild type wing vein and body color. [...]
[...] Missing individuals or erroneous information in the pedigree further hinders analysis. Modern genetic linkage are particularly useful, as it can be examined in collaboration with pedigree to maximize information that can be collected to infer likely genotypes of any missing individuals. In the events where gene sequences are known, disease-causing genes could not be identified using novel PCR technique. Gene mapping allows mutated genes to be cloned from their map position through chromosome walking from nearby gene marker. This involves using nearby DNA marker as probe to identify DNA clone that hybridizes to it. [...]
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